Digital subscriber line (DSL) technologies can provide large bandwidth for digital communications over existing subscriber lines. DSL includes a family of technologies such as Asymmetric DSL (ADSL), Asymmetric DSL 2 (ADSL2), Asymmetric DSL 2 Plus (ADSL2+), Very High Speed DSL 2 (VDSL2). G.fast is a new DSL technology, which is being developed by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T), and G.fast is the ITU-T project name. Some DSL technologies, such as ADSL, VDSL, and G.fast, may use a discrete multi-tone (DMT) line code that allocates a plurality of bits for each sub-carrier or tone in each DMT symbol. Instead of using frequency-division duplexing (FDD) in legacy DSL systems, G.fast may use synchronous time-division duplexing (STDD), which may indicate that upstream (US) and downstream (DS) DMT symbols are transmitted in different time slots. Further, in STDD data symbols for different subscriber lines in a vectored group of subscriber lines may be synchronized.
In practice, many DSL customers may be used to DSL links that are always ready and DSL modems that are always on. Statistically, a DSL link may be idle most of time, during which power is wasted. Power saving states may be designed such that the transceivers can reduce their power consumption.